1 Internet Service DNS & BIND OPS335 Seneca College of Applied Technology

2 What is DNS? DNS is a hierachical,distributed database for resolving Host Name to IP and vice versa DNS contains information for – Mapping registered full qualify domain name of host computers to IP addresses – Mapping registered network address to FQDN – Routing electronic mails – Other internet applications

3 Hierarchical Namespace Partitioned into divisions

4 Fully Qualified Domain Names Fully Qualified Domain Names: – A domain name ends in a dot e.g. cs.senecac.on.ca.cs.senecac.on.ca – a.k.a. absolute domain name a.k.a – Host name: – zenit, my – Domain Name: – zenit.senecac.on.ca., my.senecacollege.ca

5 Generic Domains Top-level domains ● com. - commerical organizations ● edu. - education institutions ● gov. - Government institutions ● net. - major network support centres ● org. - non-profit organizations ● country code – ISO letter country domain ● Others...

6 DNS Servers DNS Server: – Maps domain names to IP addresses – Holds a portions of the name-to-address mapping database – Answers queries requested from other name servers, or clients, called resolver – Maps IP addresses to domain names (pointer query)

7 in-addr.arpa domain in-addr.arpa domain (for IPv4) – Is the name space for reverse mapping – Each label can only take the decimal number 0 to 255 – Host with IP address a.b.c.d will be represented as d.c.b.a.in-addr.arpaa.b.c.d d.c.b.a.in-addr.arpa e.g. IP > in-addr.arpa

8 Distributed Name Space ● Domain and subdomain ● Zones of authority – group of symbolic name ● Name server – maintains a database of symbolic names and IP addresses and provides service of mapping between symbolic names and IP addresses. ● Delegate authority – for sub-domain ● Root Name servers – authority for the top level zone “.”

9 Domain Name Resolution ● A user program issues a request to the resolver ● The resolver formulates a query to the name server ● Name server checks its authoritative database or cache, and/or query other available name servers, starting from the root name server ● User program get the answer or an error

10 Different type of Name Server ● Caching Only Name Server (needs hint file) ● Authoritative Name Server (needs zone file(s)) ● Combination of both

11 Full Resolver User Program Full Resolver Name Server Cache Database Other Name Server Cache User Query Query Response

12 Authoritative Name Server User Program Full Resolver Auth. Name Server Cache Database User Query Query Response

13 Caching Name Server User Program Full Resolver Caching Name Server Cache Other Name Server Cache User Query Query Response (hint file)

14 Mixed-Mode Name Server User Program Full Resolver Name Server Cache Database Other Name Server Cache User Query Query Response

15 Resover Query/Response ● Query: – Recursive – Iterative (non-recursive) ● Response – Authoritative – Non-authoritative

16 Name Servers ● Primary Name Server – Read zone data from some local files and has authority over the zone. ● Secondary Name Servers – Has authority for a zone, but obtains its zone information from a primary name server by the zone transfer process ● Caching-only name server – Cache DNS info queried from other NS

17 Resource Records in Zone File ● Basic component of the DNS distributed Database ● Divided into classes for different kinds of networks ● IN – internet class e.g. SOA, A, NS, CNAME, MX, PTR ● Each zone must have SOA and NS records

18 RR Format ● Name: domain name to be defined ● TTL: Time-to-live in seconds (cache limit) ● Class: IN ● Type: Resource record type ● Rdata: value of the record (depends on type) Name TTL ClassTypeRdata

19 RR Examples ● SOA Record – Start of IN SOA abc.mydomain.ca root.abc.mydomain.ca (abc.mydomain.caroot.abc.mydomain.ca ;serial no 3600 ;refresh 600 ;retry ;expire 86400) ;minimum The above five numbers are used by slave server.

20 RR Examples 2 More: cs.senecac.on.cacs.senecac.on.ca. IN A senecac.on.casenecac.on.ca. IN MX 10 mail 23 IN PTR scs senecac.on.casenecac.on.ca IN NS prime scs IN CNAME cs

21 Setup your own Domain ● What is Domain Name Registration? ● What Domain Name is available? ● How do you register your Domain Name? ● How to setup your Name server? ● How to make your name server visible on the Internet?

22 Pick Your Own Domain Domain Names: ● A sequence of labels separated by dots ● Label: a-z, A-Z, 0-9, - and _ e.g. pod1.com, pod2.com, etc

23 How to register? ● What is your Domain Name? ● How many labels are there in your Domain Name? ● Remove the first label on the left of your domain name and the remaining is your parent domain. ● Who has authority on your parent domain? ● Go register with that authority.

24 How to setup your domain? ● Setup a Primary Namer Server (Bind 9.2.1) ● Create forward lookup zone file(s) ● Create reverse lookup zone file(s) ● Populate your zone files with – SOA record – A records – PTR records – NS records – MX records

25 Make your NS visible ● Tell people about the IP address of your Name Server. ● Test your name server. ● Ask the DNS administrator of your parent domain to delegate the zone for your domain to your name server. ● Test your Name Server on Internet. ● Mission accomplished!

26 Troubleshooting DNS Nslookup (Interactive mode) Set options: novc nodebug nod2 search recurse timeout = 0 retry = 2 port = 53 querytype = A class = IN srchlist = senecac.on.ca

27 DNS Troubleshooting nslookup ● set type=value – A, CNAME, MX, SOA, NS, PTR, ANY ● set debug - Turn debugging mode on. A lot more information is printed about the packet sent to the server and the resulting answer. (Default = nodebug)

28 DNS Troubleshooting nslookup ● Set norecurse - Tell the name server NOT to query other servers if it does not have the information. (Default = recurse; abbreviation = [no] rec) rndc- name server control utility – reload, status, dumpdb,

29 DNS Tools The following utilities come with bind-utils package: ● nslookup ● dig ● host ● Consult the man for details.

30 RFCs ● 1032 – Domain Administrator's Guide ● 1033 – Domain Administrator Operation Guide ● 1034 – Domain Names – Concepts and Facilities ● 1035 – Domain Names – Implementation and Specification ● 1713 – Tools for DNS debugging ● 1912 – Common DNS operational and Config. Errors Plus “rpm -ql bind | grep rfc”

31 DNS Q & A